Process of impregnating paper containing synthetic fibers and an amine formaldehyde precondensate with a film forming linear copolyamide



July 21, 1964 s v. MAREK ETAL 3,141,812

FIBERS AND AN AMINE FORMALDEHYDE PRECONDENSATE WITH A FILM FORMING LINEAR COPOLYAMIDE AMINE'FORMALDEHYDE PRECONDENSATE I (WATER-SOLUBLE POLY- VALENT METAL SALT) DRYING Filed Aug. 23. 1961 AQUEOUS FIBRE SLURRY *CONTAlNlNG MAN MADE'FIBRES (moss LINKING AGENT) QuEo s- \Lc oH0L c cum N mm G COPOLYAMIDE IMPREGNATIN 1 (HYDROPHBISiNG SUBSTANCE) l mnzeumowas DRYlNG 1 DRIED PAPER (HOT CALENDERING) FINlSHED PAPER I United States Patent 3,141,812 PRGCESS ()F MPREGNATING PAPER CONTAIN- ENG SYNTHETIC FHBERS AND AN AMINE FORMALDEHYDE PRECONDENSATE WITH A FHLM FGRMKNG LINEAR COPULYAMTDE Bruno Stefan Vladimir Marelr and Josef Gneisz, both of Emmenbruecke, near Lucerne, Switzerland, assignors to Societe de La Viscose Suisse, Emmenhrueke, Switzerland, a Swiss body corporate Filed Aug. 23, 1961, Ser. No. 133,304 Claims priority, application Great Britain Sept. 1, 1960 13 Claims. (Cl. 162-135) The present invention provides a process for making paper which consists at least partially of synthetic fibres and is ink-fast and has a high wet-strength, wherein the fibre material is converted into an aqueous suspension from which a sheet is formed which is then dried, impregnated, immediately dried and, if desired, pressed with the application of heat.

For the purpose of the present process the term paper designates any paper or paper-like material prepared on a paper-making machine such as paper, bonded fabric, non-woven fabric and similar flat material.

Various processes are known for the manufacture of papers and paper-like materials consisting exclusively of synthetic fibre material. On the other hand, diificulties are involved in the manufacture of such products from mixtures of synthetic, artificial and native cellulosic fibres such as wood pulp and rags, owing to the fact that the former have no fibrilling capacity and to the dissimilar physical and chemical behaviour of the fibre components.

In British Patent No. 874,249 there has been described a process by which it is possible to manufacture cellulosic papers and paper-like materials having excellent mechanical properties by using modified polyamide resins, such as N-alkoxypolyamide, as bonding agent. In this paper and paper-like material containingpolyamide fibres it is possible to vary independently, and/or improve simultaneously, the mechanical strength and the porosity by varying the conditions under which the process is performed, more especially by varying, and if desired completely omitting, the content of polyamide fibres. However, notwithstanding the good results achieved by it, said process involves certain difiiculties. Thus, to ensure sufiicient solubility of the N-alkoxypolyamide it has to be relatively highly substituted, which in the subsequent operations may under certain circumstances cause trouble by the elimination of formaldehyde and cause the paper to stick during the hot-pressing operation.

It is an object of the present invention to provide an improvement of the process described above by eliminating the aforementioned difiiculties and yielding products having improved properties.

According to the present invention there is provided a process for the production of paper which contains a proportion of synthetic fibres which comprises forming an aqueous fibre suspension which contains the synthetic fibres, an amine-formaldehyde precondensate and optionally a water-soluble polyvalent metal salt, forming a web from such suspension, drying it, impregnating the dried web with an aqueous alcoholic solution containing a linear copolyamide of high molecular weight and optionally a cross-linking substance and/or a hydrophobising agent capable of reacting chemically Withthe substratum and with the copolyamide, the impregnated sheet then being dried and, if desired, hot calendered. The term synthetic fibres is used in this specification in the generally accepted sense of including both fibres made from natural polymers, as for example viscose fibres, and those made from synthetic polymers such as polyamides.

The synthetic fibres preferably have a titre of 1.5-3 denier and a staple length of 24 mm. in the case of 3,141,812 Patented July 21, 1964 fibres derived from natural polymers, and a titre of 1.53 denier and a staple length of 3-6 mm. in the case of fibres made from wholly synthetic polymers, and may be combined with the known substances used in making paper, such as rags, bleached or unbleached wood pulp or the like. Preferred mixtures contain 20-80% by weight of synthetic fibres and 80-20% by weight of such other fibrous materials.

The copolyamides to be used in the treatment of the dried sheet should be readily soluble in aqueous alcohol, they should be colourless and above all their solutions should be stable and have little gelling tendency at room temperature. Such copolyamides are good film-formers and melt at a relatively low temperature.

The reduced viscosity mentioned hereinafter is defined by the formula:

ln 1 rel.

(where 1n represents the natural or Napierian logarithm,

1; rel. the relative viscosity and c the concentration of the solution in grams per 100 ccs. of solution) measured at 20 C. in a solution of the copolyamide of a concentration 0:0.2 gram copolyamide per 100 cc. of solution. The solvent is sulphuric acid of 93.7% strength.

Among the aforementioned copolyamides those are particularly suitable for use in the present process which can be prepared by polymerising a mixture of a salt of a diamine and a dicarboxylic acid with a lactam of an toacid. The binary copolyamides of hexamethylene diamaminocarboxylic acid and/or with an aminocarboxylic acid. The binary copolyamides of hexamethylene diammonium adipate and e-aminocaprolactam within the range of 3545% by weight of hexamethylene diammonium adipate and 6555% by weight of e-aminocaprolactam are particularly suitable. For the preparation of ternary copolyamides there may be used, for example, mixtures of 10-20% by weight of w-aminoundecylic acid, 4030% by weight of hexamethylene diammonium adipate and 50% by Weight of e-aminocaprolactam. Such copolyamides should have, for example, a reduced viscosity of 1.10 to 1.30 and, according to the proportions used, a melting point of 165-185 C. After a preliminary partial swelling at room temperature they dissolve at 60 C. in 67% aqueous ethanol or methanol -togive solutions of 8 to 12% strength. These solutions are clear and viscous and do not gel even after standing for several days at room temperature. On the other hand a solution of 10% by weight strength inalcohol gels after a few hours. A film obtained from a 7.5% solution is clear, tough and stretchable; the films have a breaking length of 1.7 to 2.5 kilometres and an elongation at break of to 300%.

It has proved particularly advantageous to add to the paper pulp a reagent capable of cross-linking the copolyamide added to the paper base by the impregnation. For this purpose it is of advantage to use a cationic melamineformaldehyde precondensate having aflinity for the fibre, if desired in the presence of a small amount of aluminium sulphate. Such a precondensate can be obtained by dissolving trimethylol-melamine in Water, adding formic or hydrochloric acid to this solution and letting it ripen for several hours until it displays a bluish opalescence. Such a solution is stable for 12 to 14 hours.

The cross-linking of the substratum with the copolyamide and/ or of the copolyamide alone may be achieved, with the application of heat and pressure. A small amount of a catalyst may be added consisting of a hydrated salt of a multivalent metal cation soluble in aqueous alcohol which develops acid proper-ties at higher temperatures during hot calendering, such as aluminium nitrate or zinc nitrate.

For the purpose of further improving the wet strength or stability to water respectively a small amount of a crosslinking substance, such as 1:6-hexarnethylene-N:N-bis- (ethyleneurea) or formaldehyde donors, and/ or of a hydrophobising agent which likewise reacts chemically with the substratum and the copolyamide, such as octadecyl ethyleneurea, may be added to the impregnating liquor. Such additives must be compatible with the dissolved copolyamide, that is to say they must not precipitate from the copolyamide solution or be inactivated by it. When an imine is present, no acidic catalyst should be present, since otherwise the ethyleneimine derivatives would precipitate from the aqueous alcoholic solution or be inactivated by it.

The use of ethyleneimine compounds is known. Inter alia, German Patent No. 880,740 discloses a process for improving fibrous materials, such as paper consisting of 100% bleached sulphite cellulose or of 100% unbleached cellulose, by treatment with a solution of an ethyleneimine derivative. These papers are dried in the usual manner on a drying cylinder at 100 C.

According to the present process, on the other hand, paper made from a mixture of synthetic fibres with cellulose fibres in the presence of an amine-formaldehyde precondensate is treated with an aqueous-alcoholic solution of a copolyamide, if desired with the further addition of an octadecyl ethyleneurea not disclosed in the said German patent, in the presence of an ethyleneimine derivative, then dried and, if desired, hot calendered.

. The process is illustrated in the accompanying drawing by a flow diagram in which the continuous lines indicate the main features of the invention and the discontinuous lines indicate subordinate features.

The following examples will serve to illustrate the invention:

Example I 650 grams (dry weight) of bleached sulphate cellulose were disintegrated by means of a high speed stirrer for 2 3 minutes in a small vessel containing 25 litres of water. In a second vessel 475 grams (dry weight) of bleached pine sulphite cellulose and 475 grams (dry weight) of bleached aspen sulphite cellulose were disintegrated in the course of hour in 75 litres of water and then ground for one hour. The sulphate cellulose suspension Was then added to the suspension of the pine and aspen sulphite cellulose; finally 400 grams (dry weight) of fibres, previously swelled in 20 litres of water, of polyhexamethylene adipamide having a titre of 3 denier and a staple length of 6 mm. were added. The combined suspensions were made up with water to a total volume of 200 litres and there were added to the whole 62 grams of alum in the form of an aqueous suspension of 15 strength and a solution of a melamine-formaldehyde precondensate. The latter solution was prepared by dissolving 60 grams of trimethylol-melamine in 750 cc. of water and 15 cc. of formic acid with stirring: the solution was left to stand until it developed a bluish opalescence, then made up with water to 2 litres and added to the suspension of the fibrous materials.

The pH value of the aqueous suspension in the stuff chest of the paper-making machine was between and 6. From this suspension a paper web was formed on a papermaking machine (Fourdrinier) and then dried. The paper-making machine was set for making a paper weighing 70-75 grams per sq. m. and having an average thickness of 0.19 mm.

Sheets of the paper manufactured in this manner were impregnated with a solution of 1 1% by weight strength in ethanol of 67% by weight strength of a copolyamide prepared from a mixture of 40% by weight of hexamethylene diammonium adipate and 60% by weight of re-aminocaprolactam (reduced viscosity of the copolyamide: 1.18; melting point: 180 C.), dried and pressed at 180 C. for one second.

The .paper treated in this manner had a relative wetstrength of 40% and in the dry state a breaking length of 6700 metres. A comparable paper prepared under identical conditions, but without addition of trimethylolmelamine precondensate, impregnated, dried and pressed for one second at 180 C. had a relative wet-strength of 2.1% and an average breaking length in the dry state of 6050 metres.

Example II Sheets of paper made as described in Example I, in the unimpregnated state, were impregnated with a solution of 11% by weight strength of the copolyamide used in Example I, prepared from a mixture of 40% by weight of hexamethylene diammonium adipate and 60% by weight of e-aminocaprolactam (reduced viscosity 1.18), 1.5% by weight of 1:6-hexamethy1ene-N:N' bis-(ethyleneurea) and 0.75% by weight of octadecyl ethyleneurea in aqueous ethanol of 67% strength and then dried on a steam-heated cylinder. The dried paper had a relative Wet-strength of 44% and in the dry state a breaking length of 6000 metres. A comparable paper made in the same Way but without addition of melamine-formaldehyde precondensate, impregnated and dried, possessed a relative wet-strength of 24% and a breaking length of 6350 metres in the dry state.

Example III Paper manufactured as described in Example I, in the unimpregnated state, but part containing and part not containing percondensate, was impregnated with a solution of 11% by Weight strength of the copolyamide used in Example I prepared from a mixture of 40% by weight of hexamethylene diammonium adipate and 60% by weight of re-aminocaprolactam (reduced viscosity 1.18) and 0.75% by weight of octadecyl ethyleneurea in aqueous ethanol of 67% strength, dried on a steam-heated cylinder and pressed at 180 C. One lot of this paper was merely dried while another was dried and hot-pressed at 180 C. for one second. The properties of these papers are shown in the following table:

1 Wet breaking length as a percentage of dry breaking length. 2 Increase of wet strength with precondensate is calculated as:

Percent wet strength with precondensate" X Percent Wet strength without precondensate Example IV A suspension was prepared in 100 litres of water of 800 grams (dry weight) of previously ground, bleached sulphate cellulose and 400 grams (dry weight) of previously ground, bleached aspen sulphite cellulose. To this suspension were then added 800 grams (dry weight) of fibres, previously swelled in 40 litres of water, of polyhexamethylene adipamide having a titre of 2 denier and a staple length of 4 mm. The whole was then made up with water to 200 litres. 62 grams of alum in the form of an aqueous solution of 15% strength and with a solution of a melamine-formaldehyde precondensate were then added to the fibre suspension. The latter solution was prepared by dissolving 40 grams of trimethylolmelamine in 500 cc. of water and 10 cc. of formic acid with stirring; the solution was left to stand until it displayed a bluish opalescence, made up with water to 2 litres and added to the suspension of the fibrous materials.

Of two dried sheets of the paper prepared in this manner but not yet impregnated, one sheet was impregnated with a solution of strength of the copolyamide used .in Example I prepared from a mixture of 40% by weight viscosity 1.30) in aqueous ethanol of 67% strength. The

impregnated sheets were dried on a steam-heated drying cylinder and pressed for one second at 165 C.

The properties of the papers manufactured in this manner are shown in the table below. The binary 40/60 coplyamide melting at 180 C. is referred to in the table by A and the ternary 10/40/50 copolyamide melting at 168 C. by B:

1 Wet breaking length as a percentage of dry breaking length.

2 Elmendorf tear in the longitudinal machine direction, in grams, corrected for a paper weight 01 100 grams per square metre.

As will be seen by comparing the data in the foregoing table it is possible to manufacture by impregnation with the ternary copolyamide B (solution of 8.75%) papers with higher breaking strengths and elongations than papers impregnated with the binary copolyamide A (solution of 10%) and having still high Elmendorf tear values.

Paper, as aforesaid, which has been conditioned for 24 hours at 20 C. and then immersed for one hour in water of 20 C. displays an increase in its length of 0.156% in the machine direction and of 1.732% in the transverse direction, and after further conditioning for 24 hours at 20 C. a shrinkage of 0.314%f Example V By the process described in Example IV a paper was made from an aqueous suspension containing 400 grams (dry weight) of previously disintegrated rags, 1600 grams (dry weight) of viscose rayon fibres previously swelled in water, having a titre of 1.5 deniers and a staple length of 4 mm., 62 grams of alum and 60 grams of trimethylolmelamine. The dried, not yet impregnated, paper was treated with a solution of 10% by weight of the copolyamide, described in Example I, prepared from a mixture of 40% by weight of hexamethylene diammonium adipate and 60% by weight of e-aminocaprolactam in aqueous ethanol of 67% strength, then dried on a steamheated drying cylinder and pressed at 170 C. The paper treated in this manner had a relative wet-strength of and a breaking length of 5420 metres in the dry state.

Example Vl In the manner described in Example IV paper was made from an aqueous suspension containing 400 grams (dry weight) of previously disintegrated rags, 1000 grams (dry Weight) of viscose rayon fibers previously swelled in water, having a titre of 1.5 deniers and a staple length of 4 mm., 600 grams (dry weight) of fibers, previously swelled in water, of polyhexamethylene adipamide, having a titre of 2 deniers and a staple length of 4 mm., 62 grams of alum and 60 grams of trimethylolmelamine.

6 The dried, not yet impregnated, paper was then treated with a solution containing 10% by weight of the copolyamide, described in Example I, prepared from a mixture of 40% by weight of hexamethylene diammonium adipate and 60% by weight of e-aminocaprolactam in aqueous ethanol of 67% strength, dried on a steamheated drying cylinder and pressed at 170 C. This paper had a relative wet-strength of 52% and a breaking length (dry) of 5000 metres.

Example VII Papers prepared as described in Examples V and VI, but not yet impregnated, were treated with the solution described in Example III of a copolyamide prepared from a mixture of 40% by weight of hexamethylene diammonium adipate and 60% by weight of e-aminocaprolactam and 0.75% by weight of octadecyl ethyleneurea in aqueous ethanol of 67% strength, then dried and pressed at 170 C.

Comparative test specimens of papers treated in this manner and of papers prepared as described in Examples II and III were immersed in each case for 4 hours in water, in hydrochloric acid of 4% strength, in alkali solution of 4% strength and in organic solvents such as benzene, alcohol and trichloroethylene. The immersed specimens remained stable towards these liquids; after having been washed and dried they were fast to ink and drawing ink.

We claim:

1. In a process for the production of paper which contains a proportion of synthetic fibres and in which an aqueous suspension of the fibre containing an amineformaldehyde precondensate is formed into a web and dried, the improvement which consists in impregnating the dried web with an aqueous-alcoholic solution containing 812% by weight of said solution of a film-forming linear copolyamide and drying the impregnated sheet.

2. Process according to claim 1, wherein the fibres used comprise 20 to of synthetic fibres. v

3. In a process for the production of paper which contains a proportion of synthetic fibres and in which an aqueous suspension of the fibre containing an amineformaldehyde precondensate and a water-soluble salt of a polyvalent metal is formed into a web and dried, the improvement which consists in impregnating the dried web with an aqueous-alcoholic solution containing 8-12% by weight of said solution of a film-forming linear copolyamide and drying the impregnated sheet.

4. In a process for the production of paper which contains a proportion of synthetic fibres and in which an aqueous suspension of the fibre containing an amine formaldehyde precondensate is formed into a web and dried, the improvement which consists in impregnating the dried web with an aqueous-alcoholic solution containing 812% by weight of said solution of a filmforming linear copolyamide and a cross-linking agent and drying the impregnated sheet.

5. In a process for the production of paper which contains a proportion of synthetic fibres and in which an aqueous suspension of the fibre containing an amineformaldehyde precondensate and aluminium sulphate is formed into a web and dried, the improvement which consists in impregnating the dried web with an aqueousalcoholic solution containing 812% by weight of said solution of a film-forming linear copolyamide and a cross-linking agent and drying the impregnated sheet.

6. In a process for the production of paper which contains a proportion of synthetic fibres and in which an aqueous suspension of the fibre containing an amineformaldehyde precondensate and aluminium sulphate is formed into a web and dried, the improvement which consists in impregnating the dried web with an aqueousalcoholic solution containing 8-12 by weight of said solution of a film-forming linear copolyamide and a hydrophobising substance and drying the impregnated sheet.

7. In a process for the production of paper which contains a proportion of synthetic fibres and in which an aqueous suspension of the fibre containing an amineformaldehyde precondensate and aluminium sulphate is formed into a web and dried, the improvement which consists in impregnating the dried web with an aqueousalcoholic solution containing 812% by Weight of saidsolution of a film-forming linear copolyamide and a hydrophobising substance reactive chemically with both the material of the web and the copolyamide and drying the impregnated sheet.

8. In a process for the production of paper which contains a proportion of synthetic fibres and in which an aqueous suspension of the fibre containing an amineformaldehyde precondensate and aluminium sulphate is formed into a Web and dried, the improvement which consists in impregnating the dried web with an aqueousalcoholic solution containing 812% by weight of said solution of a film-forming linear copolyamide and octadecylethylene urea and drying the impregnated sheet.

9. In a process for the production of paper which contains a proportion of synthetic fibres and in which an aqueous suspension of the fibre containing an amineforrnaldehyde precondensate and aluminium sulphate is formed into a web and dried, the improvement which consists in impregnating the dried web with an aqueousalcoholic solution containing 812% by weight of said solution of a film-forming linear copolyamide and a bifunctional ethylene imine derivative and drying the impregnated sheet.

10. In a process for the production of paper which contains a proportion of synthetic fibres and in which an aqueous suspension of the fibre containing an amineformaldehyde precondensate and aluminium sulphate is formed into a web and dried, the improvement which consists in impregnating the dried web with an aqueousalcoholic solution containing 8-12% by weight of said solution of a film-forming linear copolyamide and a formaldehyde donor and drying the impregnated sheet.

11. In a process for the production of paper which contains a proportion of synthetic fibres and in which an aqueous suspension of the fibre containing trimethylol melamine is formed into a web and dried, the improvement which consists in impregnating the dried web with an aqueous-alcoholic solution containing 8-12% by weight of said solution of a film-forming linear copolyamide and drying the impregnated sheet.

12. In a process for the production of paper which contains a proportion of synthetic fibres and in which an aqueous suspension of the fibre containing an amineformaldehyde precondensate is formed into a web and dried, the improvement which consists in impregnating the dried web with an aqueous-alcoholic solution containing 8-12% by weight of said solution of a filmforming linear copolyamide and drying and hot-calendering the sheet.

13. In a process for the production of paper which contains a proportion of synthetic fibres and in which an aqueous suspension of the fibre containing, based on the fibre, about 2 to 3% by weight of a polymethylol melamine is formed into a web and dried, the improvement which consists in impregnating the dried web with a film-forming linear copolyamide dissolved in aqueous alcohol at a concentration of 10% by weight and drying the impregnated sheet.

References Cited in the file of this patent UNITED STATES PATENTS 2,540,352 Schenck Feb. 6, 1951 2,559,220 Maxwell July 3, 1951 2,983,627 Williams May 9, 1961 3,000,777 Williams Sept. 19, 1961 3,016,325 Pattilloch Jan. 9, 1962 FOREIGN PATENTS 873,700 Great Britain July 26, 1961 874,249 Great Britain Aug. 2, 1961 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,141,812 July 21, 1964 Bruno Stefan Vladimir Marek et a1,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

The binary Signed and sealed this 1st day of June 1965.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents ERNEST W. SWIDER Attesting Officer 

1. IN A PROCESS FOR THE PRODUCTION OF PAPER WHICH CONTAINS A PROPORTION OF SYNTHETIC FIBRES AND IN WHICH AN AQUEOUS SUSPENSION OF THE FIBRE CONTAINING AN AMINEFORMALDEHYDE PRECONDENSATE IS FORMED INTO A WEB AND DRIED, THE IMPROVEMENT WHICH CONSISTS IN IMPREGNATING THE DRIED WEB WITH AN AQUEOUS-ALCOHOLIC SOLUTION CONTAINING 8-12% BY WEIGHT OF SAID SOLUTION OF A FILM-FORMING LINEAR COPOLYAMIDE AND DRYING THE IMPREGNATED SHEET. 